The present invention relates to a shift-assisting device for reducing the shifting force in the speed-change operation of a transmission mounted on a vehicle.
Large trucks and buses that require a large shifting force for changing the speed have been equipped with a shift-assisting device for executing the shifting operation with a decreased force. The shift-assisting device with which large vehicles are furnisheduses generally compressed air as the source of operation. The shift-assisting device that uses compressed air as the source of operation is equipped with a shift actuator comprising a pneumatic pressure cylinder that operates a speed-change operation mechanism coupled to a change lever in the same direction as the direction in which the change lever is shifted. Large vehicles generally use compressed air as the source for operating the brake and are, hence, able to use the compressed air for the shift-assisting device. However, small- and medium-sized vehicles that are not equipped with a compressor as a source of compressed air cannot be provided with a shift-assisting device that uses a shift actuator that comprises a pneumatic pressure cylinder. In recent years, however, it has been demanded to provide even small- and medium-sized vehicles with a shift-assisting device, and there have been proposed shift-assisting devices using an electric motor as disclosed in, for example, Japanese Laid-open Patent Publication (Kokai) No. 8737/1993 and Japanese Patent No. 2987121. In a shift-assisting device using an electric motor, it is desired to control the driving force of the electric motor in response to the operation of the change lever by a driver in order to conduct a smooth shifting operation. According to the shift-assisting devices disclosed in the above Japanese Laid-open Patent Publication (Kokai) No. 87237/1993 and Japanese Patent No. 2987121, the force for operating the change lever toward the direction of shift is detected, and the driving force of the electric motor is controlled according to this force of operation.
In shifting a transmission equipped with a synchronizing mechanism, the largest operation force is required for bringing the gears into engagement with a synchronized mechanism and then, a considerably large operation force is required for bringing the chamfer of the dog teeth into engagement with the chamfer for the spline of the clutch sleeve. And, in disengaging the gears, an operation force is required from the start of operation for disengaging the gears until the dog teeth are disengaged from the spline of the clutch sleeve. However, in the shift-assisting device that controls the driving force of the electric motor based on the operation force, since the electric motor is driven after the operation force has reached a predetermined value, there exists a time lag until the assisting force is produced after the operation force has increased, In executing the shifting operation, therefore, the driver feels a large force just before the assisting force is produced by the electric motor. In order to solve this problem, the present applicant has proposed in Japanese Patent Application No. 46173/2000 a shift-assisting device for a transmission which has a shift stroke sensor that detects the shift stroke position of the shifting mechanism and controls the electric motor for shift-assisting, based on a detection signal from the shift stroke sensor, so as to obtain a driving force corresponding to the shift stroke position.
In a shift-assisting device that controls an electric motor for shift-assisting to obtain a driving force corresponding to the shift stroke position, however, the electric motor is set to produce the largest assisting force when the shift stroke is positioned in the synchronizing range. It has been found that due to this, the clutch sleeve is caused to move at a high speed just after termination of the synchronization, and as a result, a phenomenon in which the clutch sleeve hits the stroke end at a high speed occurs.
It is an object of the present invention to provide a shift-assisting device for a transmission, which is capable of preventing the occurrence of the above phenomenon of the clutch sleeve in the shifting operation.
In order to accomplish the above-mentioned object, the present invention provides a shift-assisting device for a transmission comprising an electric motor for operating a speed-change operation mechanism in the same direction as the direction in which a change lever is shifted, the speed-change operation mechanism being coupled to the change lever and actuating a synchronizing mechanism of the transmission; a shift stroke sensor for detecting the shift stroke position of the speed-change operation mechanism; and a controller for outputting, to the electric motor, a signal indicative of a driving force corresponding to the shift stroke position in response to a detection signal from the shift stroke sensor;
wherein the controller comprises a gear position judging means for judging a target gear position of the transmission that is to be shifted by the change lever, and a difference-in-the-synchronized-rotational-speed detector means for detecting a difference in the synchronized rotational speed of the target gear position judged by the gear position judging means; and
when the difference in the synchronized rotational speed detected by the difference-in-the-synchronized-rotational-speed detector means is smaller than a predetermined rotational speed, the controller outputs, to the electric motor a signal indicative of a driving force smaller than the driving force that corresponds to the shift stroke position.
According to the present invention, there is further provided a shift-assisting device for a transmission, which comprises a selected position sensor for detecting the selected position of the speed-change operation mechanism and a shifting direction detector means for producing signals corresponding to the operations in a first shifting direction and in a second shifting direction of the change lever, and in which the gear position judging means judges a target gear position of the transmission, that is to be shifted by the change lever based on the selected position detected by the selected position sensor and the shifting direction detected by the shifting direction detector means.
According to the present invention, there is further provided a shift-assisting device for a transmission, which comprises an input-shaft-rotational-speed sensor for detecting the rotational speed of the input shaft of the transmission; and an output-shaft-rotational-speed sensor for detecting the rotational speed of the output shaft of the transmission; and in which the difference-in-the-synchronized-rotational-speed detector means determines the rotational speed of a speed change gear of the target gear position judged by the gear position judging means based on the target gear position judged by the gear position judging means and the rotational speed of the input shaft detected by the input-shaft-rotational-speed sensor, and obtains a difference in the synchronized rotational speed by comparing the rotational speed of the speed change gear with the rotational speed of the output shaft detected by the output-shaft-rotational-speed sensor.